Electron Scattering in Time-Dependent Density Functional Theory

TL;DR

This paper investigates the limitations of current approximate exchange-correlation functionals in time-dependent density functional theory for accurately modeling electron scattering, highlighting the importance of peak and valley structures in the potential.

Contribution

It provides detailed analysis using a model system to show how existing functionals fail to reproduce exact scattering probabilities and discusses the impact of initial state choices.

Findings

Exact functional reproduces scattering probabilities accurately.

Current approximate functionals fail to match exact scattering results.

Choice of initial Kohn-Sham state significantly affects dynamics.

Abstract

It was recently shown [Y. Suzuki, L. Lacombe, K. Watanabe, and N. T. Maitra, Phys. Rev. Lett. 119, 263401 (2017)] that peak and valley structures in the exact exchange-correlation potential of time-dependent density functional theory are crucial for accurately capturing time-resolved dynamics of electron scattering in a model one-dimensional system. Approximate functionals used today miss these structures and con- sequently underestimate the scattering probability. The dynamics can vary significantly depending on the choice of the initial Kohn-Sham state, and, with a judicious choice, a recently-proposed non-adiabatic ap- proximation provides extremely accurate dynamics on approach to the target but this ultimately also fails to capture reflection accurately. Here we provide more details, using a model of electron-He + as illustration, in both the inelastic and elastic regimes. In the elastic case, the time-resolved picture is contrasted with the time-independent picture of scattering, where the linear response theory of TDDFT can be used to extract transmission and reflection coefficients. Although the exact functional yields identical scattering probabil- ities when used in this way as it does in the time-resolved picture, we show that the currently-available approximate functionals do not, even when they have the correct asymptotic behavior.